1. Technical Field
The present invention relates to millimeter wave communication systems and, more particularly, to phase shifters for millimeter wave communication systems that make use of tunable transmission lines.
2. Description of the Related Art
Phase shifters are important components in any communication system. This is particularly true of phased array communication and radar systems, where gain may be improved by adjusting the phase shift for each of an array of antennas, such that gain is improved in a desired direction. However, existing phase shifters present challenges for use in millimeter wave (mmWave) systems.
Referring now to FIG. 1, cross-sectional diagram of a prior art tunable transmission line is shown. The capacitance of this component can be adjusted to provide phase adjustments in a phase shifter. A chip 100 has a number of crossing transmission lines 106 and 108 perpendicular to and embedded under a signal line 104 and ground lines 102. A transistor's capacitance 116 provides a variable capacitance that allows tuning. In particular, the capacitances between the signal terminal 104 and the crossing lines 106, between the crossing lines 106 and the crossing lines 108, and between crossing lines 106 and ground determine the capacitative tuning range of the device.
Conventional phased array systems inherit the flaws of the phase shifters. Large phase shifters are spaced out on the chip, such that long transmission lines are needed to connect them to a power divider. As a result, the size and complexity of the device increases.